The present invention relates generally to methods and apparatus for depositing process coatings onto substrates, and more particularly, to a control system for improving the uniformity of such coatings especially at or near the leading edge of a substrate in a batch process.
Extrusion coating is a known method of directly depositing process coating onto substrates, wafers and similar objects (collectively xe2x80x9csubstratesxe2x80x9d) in the microelectronics, display technology and related industries, including coatings for polymer fuel cells. The substrates are transported linearly beneath an extrusion coating head and process fluids are precisely dispensed from a linear orifice in the extrusion head using a microprocessor-based electrohydraulic pumping system. Depending on the particular application, such process fluids include photoresist, polyimides, color filter materials and the like. Typically, the substrate is between 100-1500 mm square and the film thickness is between 1,500 angstroms and 25 microns. Such extrusion coating techniques are well suited for research and development activities as well as high volume production requirements.
Although known extrusion systems for this type provide significant advantages as compared to other liquid deposition techniques (such as spin coating), they often suffer from a similar problemxe2x80x94the inability of the coating head to establish a uniform coating at the leading edge of the substrate during certain applications. In these systems, there is a requirement that each substrate be leveled prior to the coating process and thus the coating deposition is started and stopped with each new substrate. With such xe2x80x9cbatchxe2x80x9d processing, a coating xe2x80x9cbeadxe2x80x9d must be re-formed between the extrusion head and each new substrate to thereby xe2x80x9cwetxe2x80x9d the surfaces. When this bead initially contacts the substrate, however, it may cause a xe2x80x9cperturbationxe2x80x9d for some measurable distance (e.g., 5 mm) from the leading edge of the substrate. Sometimes a leading edge anomaly of this type dictates that the substrate be rejected completely, thus increasing material and process costs and decreasing processing efficiency.
There have been attempts in the art to address the problem of establishing a uniform coating condition in a linear or so-called slot type extrusion coater, and systems of this type are illustrated in U.S. Pat. Nos. 4,938,994 and 5,183,508. In these patents, a controlled volumetric flow rate of the liquid is delivered to a liquid containing chamber within the extrusion head and then through the applicator slot to create what is said to be a uniform volumetric flow rate of liquid exiting from each point along the slot. A displacement piston associated with the extrusion head generates a fluid pulse to control the formation of a connecting bead of the liquid coating prior to, at the same time as, or after the sending of the controlled volumetric flow rate of the liquid. This technique purports to apply a layer of the liquid with a precisely-controlled volume per unit area of the liquid to the substrate. These machines in these patents also include a slot sealing unit that cleans the extrusion head slot between applications.
The techniques illustrated in these patents do not adequately address the problem of leading edge perturbations that may affect uniformity of the coating. Indeed, primarily these patents provide useful devices for cleaning the extrusion head itself between coatings, but such cleaning does not, in and of itself, solve this problem.
There remains a long-felt-need in the industry to overcome the problem of leading edge anomalies arising during the slot type coating of substrates in a batch process.
These and other objects, features and technical advantages are achieved by a system and method which comprises a control system for an extrusion head and pump mechanism for applying a uniform layer of liquid to a substrate. The extrusion head includes a liquid-containing chamber and a slot in communication with the chamber. A pump, integrally mounted to the extrusion head itself, such as is shown in the above referenced concurrently filed, co-pending patent application entitled xe2x80x9cMoving Head, Coating Apparatus And Method,xe2x80x9d provides a steady-state fluid flow of liquid to the slot on the extrusion head. The integrally mounted pumping means enables precision control of flow conditions within the head in a manner that avoids transient perturbations during initial extrusion startup. Fluid is supplied to the pump from a fluid supply bay remotely located from the pump, or, if desired, integral with the system. The fluid supply bay includes a supply pump, a fluid reservoir and means for filtering the fluid. A substrate chuck movable between first and second positions moves the substrate relative to the extrusion head slot to provide a uniform coat of fluid to the substrate.
The control system consists of an adaptive type control unit, including a neural network system, or a programable controller. A pressure sensor within the head manifold will supply data to the control system to ensure no outgassing. A vision sensor on the substrate chuck as well as a vision sensor at the bead former on the extrusion head, preferably a CCD camera or a CCD monitoring the primary device, will provide data on the dispensation of the subject fluid to the control system. Based on these readings, the control system will control the fluid flowrate and the dispensing procedure to ensure that a smooth coating is produced. The process control system can also extend to monitoring the steady state flow from the fluid supply bay to the extrusion head as well as control the beading at the extrusion head by drawing back, if necessary, the subject fluid.
The foregoing has outlined some of the pertinent aspects of the present invention. These aspects should be construed to be merely illustrative of some of the more prominent features and applications of the invention. Many other beneficial results can be obtained by applying the disclosed invention in a different manner or modifying the invention. Accordingly, other aspects and a fuller understanding of the invention may be had by referring to the following detailed description of the preferred embodiment.
It will be appreciated by those who are skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.